The predecessor clutch actuator mechanism of U.S. Pat. No. 4,328,883, entitled "Hydraulic Actuator Mechanism for a Friction Clutch" and issued May 11, 1982, in the name of the inventor of the invention herein disclosed and claimed, provides the background for this invention. That disclosure provided an earlier designed hydraulic pressure operated mechanism disposed between the master cylinder manual clutch operator and the clutch throw out bearing. Other related patents are included in the patent references made of record in the above-noted U.S. patent.
The clutch actuator mechanism of the above-noted U.S. patent mounts the hydraulic clutch actuator about the clutch output shaft and bearing retainer. The hydraulic clutch actuator is secured to the end wall or cover plate of the clutch bell housing. Because the member transmitting forces from the hydraulically actuated pistons of the actuator to the throw out bearing is secured to the pistons, and that member also receives the clutch output shaft through a circular, completely encompassed, opening, and the actuator is secured to the end wall or cover plate, the only way that the actuator can be removed for repair or replacement is to remove the transmission from the clutch housing. This involves disconnecting the transmission output shaft from the drive shaft leading to the differential of a typical rear wheel drive automobile, or the constant velocity joints and shafts of a front wheel drive automobile, moving the transmission rearwardly to remove its input shaft (which is the clutch output shaft) from the clutch housing, dropping the transmission so as to access the clutch housing cover plate, removing the mounting bolts holding the actuator and the bearing retainer as well as the cover plate, and sliding the actuator out of the clutch housing. In some instances, after removing the mounting bolts holding the actuator and the bearing retainer to the clutch housing end wall, those elements may then be moved through an access opening in the side, top or bottom of the clutch housing. However, this can only occur after the bearing retainer and the transmission output shaft have been removed from extending through the force transmission member connecting the hydraulic pistons to the throw out bearing. While the structure disclosed in that patent may include a sealed, ready-to-use hydraulic system which is installed in the clutch housing before the transmission is in place or is returned to its normal operative position, the actuator mechanism still cannot be installed, removed, repaired or replaced while the transmission is in its operating position in relation to the clutch housing and the clutch mechanism.
Other installations commonly found on some automotive vehicles have a hydraulic clutch master cylinder operating a servo mounted outside the transmission, with the servo stroking an intermediate rod which moves a throw out bearing fork to move the throw out bearing, all in the same manner as earlier purely lever-operated types of clutch disengagement mechanisms. Such installations have all the adverse features of such lever-operated mechanisms, and have done little if anything to improve the overall system efficiency, assembly, removal, repair and replacement of the mechanism within the clutch housing.